Maraging steels are carbon-free iron alloys that are strengthened through precipitation hardening rather than carbon content. They contain additions of nickel, cobalt, molybdenum, titanium, and aluminum. Maraging steels are heat treated through solution treatment to form a martensitic structure, followed by aging to precipitate hardening intermetallic compounds within the martensite. This provides maraging steels with ultra-high strength even at elevated temperatures, along with excellent toughness. Common applications include aerospace components, ordnance, and tooling due to their combination of high strength, corrosion resistance, and fatigue endurance.

1. Maraging Steel
1. Introduction and General Characteristics:
 Maraging steels are characterized with superior strength
combined with excellent toughness properties and
weldability. without loss of malleability. OR
 Maraging steels are carbon free iron-nickel alloys with
additions of cobalt, molybdenum, titanium and aluminium.
 The term maraging is derived from the strengthening
mechanism, which is transforming the alloy to martensite
with subsequent age hardening. (Martensite + Ageing)
• special class of steel contain No-carbon but provides “ultra-
high-strength”
• Their strength comes from precipitation of intermetallic
compounds like (Mo, Ti & Al)Ni3 “NOT FROM CARBON”.
• High strength is maintained up to 350 oC. …? How?

2. cont…
• Since ductile Fe-Ni martensites are formed upon cooling,
cracks are non-existent or negligible.
• These steels can be nitrided to improve case hardness.
• C is considered as an impurity element in these steel and it
should be kept below 0.03%.
2. Application:
• Considered as Military grade … crankshafts, gears, and the
firing pins of automatic weapons that cycle from hot to cool
repeatedly under substantial load.
• Missile Nose. aerospace, e.g. undercarriage parts and wing
fittings, tooling & machinery , e.g. extrusion press rams and
mandrels in tube production, gears
• Ordnance components and fasteners.

3. 3. Types of Maraging Steels Well known grades 18%, 20% & 25%

4. 4. Production of Maraging Steel
E.A.F/ V.I.M
L.F
V.D/V.C.D
I.C
V.A.R
Shaping (Rolling/Forging )
Solution Treatment + Ageing
Nitriding (If Required)
Most Important
Step

5. 5. Heat Treatment of Maraging Steel:
Solution
Treatment
+
Aging

6. 6. Physical Metallurgy of Maraging Steel /
• Effects
a) Ni = Austenitic Stabilizing Element, Increases hardenability, resistant to fatigue &
corrosion
b) Co/Mo = Retain hardness at high temperature, good wear resistant.
c) Ti = Stabilize Ferrite, Refine Grain structure, raises creep strength.
d) Al = stabilize ferrite, form nitride, refine grain size.
Element 200 250 300 350
Substitutional Element Ni 17-19 17-19 18-19 18-19
Substitutional Element Co 8-9 7-8.5 8.5-9.5 11.5-12.5
Substitutional Element Mo 3-3.5 4.5-5.2 4.6-5.2 4.6-5.2
Substitutional Element
(Partially Soluble)
Ti 0.15-0.25 0.3-0.5 0.5-0.8 1.3-1.6
Substitutional Element Al 0.05-0.15 0.3-0.5 0.5-0.8 1.3-1.6
Substitutional Element Fe Balance Balance Balance Balance
• 18%Ni Maraging Steel Grades

7. 6.1 Fe-Ni Phase Diagram

8. • steels are solution treated at 820 oC , to absorb all
precipitates or alloying elements & produce uniform
austenitic structure.
• upon cooling in air/quenching, an Fe-Ni BCC Martensite is
formed instead of ordinary Tetragonal Martensite (Fe-C).
• This is of lath-like BCC form, softer & tougher than ordinary
martensite but heavily dislocated martensite.
(means high dislocation density = high energy = means
favorable site for precipitation)
• Upon ageing at 480oC for 3 or more hours, coherent
precipitates of intermetallic compound (Mo, Ti & Al)Ni3 are
formed.
• The main function of “Co” seems to produce more sites for
the nucleation of (Mo, Ti & Al)Ni3 precipitates. Or Co reduces
the solubility of Ti, Mo & Al in the matrix as a result theses
increases the volume fraction of rich precipitate.

10. • If the precipitation hardening temperaure exceeds 500oC, over-aging
results the strength begin to fall due to reversion of the austenite.
• similarly increases the time for aging the same effect will be
produce.

11. Why Ni is selected for Maraging steels ?
How it can with stand high strength at high temperature?
• High-nickel steels introduces considerable thermal hysteresis
in the polymorphic transformation.
• steel containing 15% nickel will not begin to transform on
cooling until a temperature of about 250oC has been reached,
when martensite begins to form.
• On re-heating the structure, however, martensite does not
begin to change to austenite until a temperature approaching
600oC.
• This hysteresis, or lag, in transformation is fundamental to the
use of nickel in maraging steels.